The variable, n, represents a number that a spectator chooses. what is the result after the calculation of 2n + 4 – n – 4?

I'm at a bookstore with $\$35$ in my pocket and a $20\%$-off coupon. what is the cost of the most expensive book i can buy with my money and the coupon? (assume that there are books of every possible price in the bookstore. it's a large bookstore! )